1. Field of the Invention
The present invention relates to the field of x-ray inspection systems.
2. Prior Art
Inspection systems such as x-ray inspection systems and visual inspection systems are now frequently used for the inspection of various products. Of particular interest for the present invention is the inspection of products such as printed circuit boards having various electronic components physically and electrically connected thereto, generally referred to herein as populated boards or populated printed circuit boards. Such inspection, which frequently is at least partially automated, will detect missing components and solder bridges, and allow the evaluation of solder flow and bonding of device terminals to the printed circuit board. Certain features may readily be detected by a camera responsive to visible light (hereinafter referred to as the xe2x80x9cvisual imagexe2x80x9d or xe2x80x9cvisual cameraxe2x80x9d). Other features, particularly those which are shaded or sheltered by the devices themselves, may be detected by a camera responsive to the x-ray image created by the passing of x-rays through the printed circuit board and devices thereon from an x-ray source supported by some transport system on the side of the populated board opposite the camera (hereinafter referred to as the xe2x80x9cx-ray imagexe2x80x9d or xe2x80x9cx-ray cameraxe2x80x9d). In some cases, features of the populated board being inspected can be better inspected by misaligning the x-ray source and the x-ray camera so that the x-ray image is created by x-rays passing through the printed circuit board at an angle other than 90xc2x0. In still other instances, aspects of features can be best evaluated by combining the x-ray image and the visual image to extract information not readily discernable from either image alone.
U.S. Pat. No. 5,541,856 discloses an x-ray source transport system providing for x and y translation of the x-ray source. Such a system should perform well and has the advantage that device positions, etc. on the populated board are normally defined by x and y coordinates, not rho-theta coordinates. However, because such systems are generally processor controlled, conversion of inputs or commands from one coordinate system to another does not involve any additional cost or time delay. Also, coupling power and control signals through an x-y translation system, which in normal use frequently translates over most of its full range, can result in substantial design and reliability problems. By way of example, a single cable from a stationary part of the system to the x-ray source is subject to both abrasion and fatigue, requiring more maintenance than desired. Separate cabling for each translation system also presents its own problems in both design and reliability.
Inspection systems with rho-theta x-ray source motion for inspection of populated printed circuit boards and the like are disclosed. The inspection systems include a transport system for transporting articles to be inspected into and out of the inspection system. An x-ray source is mounted on a first radial translation system adjacent one side of the article to be inspected for translation along an axis parallel to the article to be inspected. The first radial translation system is rotatably mounted about an axis perpendicular to the article to be inspected so that the x-ray source may be positioned and moved anywhere within an area by proper coordination of the angle of rotation of the rotary transport system and the radial translational position of the first translational system. The exemplary embodiment disclosed also includes a second translational system supported on the first translational system for movement of the x-ray source in a direction parallel to the axis of rotation of the rotary transport system. The use of the combination of radial translation and angular rotation for positioning of the x-ray source simplifies the coupling of power and control signals to the x-ray source and transport motors and controls.